1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine, a facsimile machine or a printer.
2. Description of the Related Art
Heretofore, a device for electrostatically charging a drum-type electrophotographic photoconductor or photosensitive body (hereinafter referred to as “photosensitive drum” for brevity) has been composed of a corona charging device designed to expose a surface of a photosensitive drum to corona discharge so as to electrostatically charge the surface. Late years, from the aspect of advantages in lower-level ozone formation and lower power consumption as compared with the corona charging device, a contact charging device designed to bring a charging member in a voltage-applied state into contact with a surface of a photosensitive drum so as to electrostatically charge the surface has come into practical use.
Further, in place of selenium or OPC (Organic Photo Conductor) conventionally used as a material for a surface layer of a photosensitive drum, amorphous silicon is recently beginning to be used in view of environmental concerns, longer life duration, etc.
While amorphous silicon has excellent properties, it has difficulty in being formed as a homogeneous or uniform film due to its production process. Thus, a surface layer of a photosensitive drum formed of such a film is likely to have a locally uneven charge storage capacity which causes an uneven electrostatically-charged state in an axial direction of the photosensitive drum (hereinafter referred to as “axially uneven charge-distribution”), for example, a phenomenon that one end of the photosensitive drum is easily charged and the other end is hardly charged.
As one of measures for suppressing the axially uneven charge-distribution, there has been proposed a technique of providing on an upstream side of a contact charging device a charge removing device for exposing a surface of a photosensitive drum to light to perform a charge removal operation, and adjusting a width of a light path between a light source of the charge removing device and the surface of the photosensitive drum, in an width direction of the photosensitive drum, so as to control the distribution of charge-removing light intensity in the width direction of the photosensitive drum (see Japanese Patent Laid-Open Publication No. 08-272270).
The above technique will be described in more detail with reference to FIGS. 8A and 8B, wherein FIG. 8A is a top plan view of the charge removing device 30, viewing from the side of the photosensitive drum 4, and FIG. 8B is a side view of the charge removing device 30 and the photosensitive drum 4. The charge removing device 30 comprises a plurality of point light sources 301 each consisting of a LED (Light Emitting Diode), a support member 302 supporting the point light sources 301 in a line arrangement, and a pair of plate-shaped members 303 disposed in a gap between the point light sources 301 and the photosensitive drum 4 and adapted to adjust a width of a light path extending from the point light sources 301 to the photosensitive drum 4. In this technique based on adjustment of the light-path width, even a slight change of the light-path width has great impact on the distribution of charge-removing light intensity, and it is practically difficult to adequately adjust the light-path width in such a manner as to obtain a desired distribution of charge-removing light intensity. Consequently, it is likely that the photosensitive drum 4 is not electrostatically charged with sufficient uniformity (or axially uneven charge-distribution occurs).